CVE-2017-1000199 in tcmu-runner
Summary
by MITRE
tcmu-runner version 0.91 up to 1.20 is vulnerable to information disclosure in handler_qcow.so resulting in non-privileged users being able to check for existence of any file with root privileges.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-1000199 affects tcmu-runner versions 0.91 through 1.20 and represents a critical information disclosure flaw within the handler_qcow.so component. This vulnerability exposes a fundamental security weakness in how the system handles file access permissions when processing qcow2 storage images through the target core user module. The flaw allows unprivileged users to perform reconnaissance activities that would normally require elevated privileges, effectively bypassing standard access controls that should protect sensitive file system resources.
The technical implementation of this vulnerability stems from improper access control mechanisms within the qcow2 handler module. When processing storage operations, the handler_qcow.so component fails to properly validate file access requests, enabling malicious users to probe the file system for the existence of arbitrary files without possessing the necessary permissions. This occurs because the module does not adequately enforce the principle of least privilege during file system operations, particularly when handling virtualized storage images. The vulnerability manifests through specific error codes and response patterns that reveal whether targeted files exist on the system, effectively creating a side-channel information leak that provides attackers with valuable reconnaissance data.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally undermines the security model of the affected system. Non-privileged users can now perform systematic reconnaissance to identify sensitive files, directories, and system resources that would normally be protected from casual inspection. This capability enables attackers to map the target system's file structure and identify potential targets for further exploitation, including configuration files, credential stores, or other sensitive resources that may contain valuable information for privilege escalation or lateral movement. The vulnerability operates at the kernel level within the storage subsystem, making it particularly dangerous as it can be exploited without requiring direct system access or elevated privileges.
Security professionals should implement immediate mitigations including updating tcmu-runner to versions 1.2.1 or later where this vulnerability has been addressed through proper access control enforcement. The fix involves implementing stricter file access validation within the qcow2 handler module to ensure that all file operations respect the principle of least privilege and do not expose system information to unauthorized users. Additionally, system administrators should consider implementing network segmentation and access controls to limit exposure of affected systems, while monitoring for anomalous file system access patterns that may indicate exploitation attempts. This vulnerability aligns with CWE-200 (Information Exposure) and represents a classic example of how improper access control can lead to privilege escalation through information disclosure. The ATT&CK framework categorizes this under T1083 (File and Directory Discovery) and T1068 (Exploitation for Privilege Escalation) as it enables reconnaissance activities that can lead to more sophisticated attacks. Organizations should also conduct comprehensive vulnerability assessments to identify other instances of similar access control flaws within their storage subsystems and ensure proper patch management protocols are in place to prevent similar issues from arising in the future.